One of the prime movers on Romney’s behalf in this election is a four year long shift of voters who no longer consider themselves Democrats and are now either Independents or Republicans. Since 2008 about six percent of Democrats have left the Party and the GOP has gained about three points (the rest becoming Independents).

In the aftermath of their Convention, however, the Democratic Party has recovered its lost sheep. Before the two conventions, my polling indicated a three point spread between the parties — 34% Democrat v. 31% Republican. In polling on September 12-13, I found the gap had widened to ten points — 38% Democrat v. 28% Republican.

In retrospect, this was the Democratic strategy at their convention (and it succeeded brilliantly): Long ago, President Obama realized that he would never win re-election based on his dismal record and he decided to try to cast the contest as a “choice” rather than a referendum on his record in office. To win that choice, Obama has spent about $150 million on ads savaging Romney over Bain Capital, tax returns, and foreign bank accounts. But it didn’t work. In my pre-convention polling, Romney consistently led Obama by between four and seven points among likely voters.

So Obama’s people decided to base the choice on political parties not on their candidates.

That’s why Clinton rarely mentioned Romney in his speech but focused instead on the Republican Party, the GOP Congress, the Tea Party, the conservatives, the right wing…anything but Romney. And Obama’s speech was largely devoted to the contrast between the Democrats who wanted to lend you hand and the Republicans who, he said, are telling people “you’re on your own.”

And the Convention showcased all the oldies but goodies which have held the Democratic coalition together — abortion, contraception, equal pay, tax “fairness” et. al. Their strategy worked. Wandering and wayward Democrats — particularly unmarried women – came home and switched their party identification, at least for now.

As a result, Obama has had a bounce from the convention as the number of Democrats swelled.

Will the switch last? Not if the Republicans reassert their party brand. Voters still basically agree more with Republicans than with Democrats on core philosophy. Gallup asked last month which you wanted government to do? Leave you alone or lend you a hand? Voters opted by 54-35 to be left alone.

The Republican Party now needs to explain how it differs from the Democrats and draw the distinction between a party of spending, debt, welfare, and handouts and one of low taxes, less regulation, and individual responsibility.

Romney has a solid ten point lead on jobs and the economy. He has, as a result of his convention and particularly due to his wife’s speech, overcome the personal negatives with which Obama tried to saddle him in the months before the convention.

Now he must turn to the fundamentally different narrative of the two parties and explain that he wants to get government off your back, out of your pocketbook, and far away from the checkbook.

By asserting the fundamental superiority of the Republican brand over the Democratic alternative, Romney and Ryan can reverse the shift in party identification and resume their lead over Obama.